Navigation Message Bit Identification Using Coherent Code Processing

Randal K. Douglas and Walter E. Lillo

Abstract:	A navigation message bit stream is modulated on each of the GPS L1 C/A-, L1 P-, and the L2 P-code signals. To demodulate the bit stream in low noise conditions, it is sufficient to track any one of these signals with a phase-locked loop and to apply an arc-tangent rule to the inphase and quadrature correlations. Coherent replica generation, made possible by ultra-tight processing, in which all code and carrier replica signals are generated directly from the best estimate of the navigation state, allows the fusion of power from all signals for improved bit demodulation in high-noise conditions. A statistical analysis of the bit estimation problem, cast as a binary hypothesis test, predicts a 1.2 dB improvement when L1 C/A- and L1 P-codes are processed coherently. Studies performed using carefully calibrated, recorded GPS signals with applied broad-band road-jamming, confirm this analytical prediction. Statistical analysis also predicts a 1.8 dB improvement when the L2 P-code is added. An empirical verification of this prediction will be done soon. Performance is also improved when early, prompt, and late correlation weightings are chosen via a generalized eigenvector problem. In particular, only the prompt is used when in code lock.
Published in:	Proceedings of IEEE/ION PLANS 2006 April 25 - 27, 2006 Loews Coronado Resort Hotel San Diego, CA
Pages:	933 - 947
Cite this article:	Douglas, Randal K., Lillo, Walter E., "Navigation Message Bit Identification Using Coherent Code Processing," Proceedings of IEEE/ION PLANS 2006, San Diego, CA, April 2006, pp. 933-947. https://doi.org/10.1109/PLANS.2006.1650694
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